Radiation therapy is known in the art. Generally speaking, such therapy involves exposing an unwanted volume on or within a patient's body to high-energy radiation (such as, but not limited to, x-rays). This radiation often serves to destroy the irradiated cellular material and hence reduce or eliminate the unwanted volume. In many cases such radiation is periodically administered over time (days, weeks, or months).
Unfortunately, this radiation does not inherently discriminate between wanted and unwanted portions of the patient's body. Treatment plans are therefore formulated to both ensure appropriate irradiation of the unwanted volume while at least attempting, in various ways, to minimize exposing wanted volumes to the radiation. These treatment plans are often based, at least in part, upon images (such as x-ray images) that include the patient's treatment volume.
In many cases the patient's physical circumstances will change over the course of such a treatment regimen or even subsequent to planning the treatment but prior to administering that treatment. The unwanted volume itself, for example, can become reduced in size, change its orientation or shape, and/or move in some respect. As another example, the patient themselves may gain, or lose, weight. And as yet another example, other structures within the patient can change shape, location, or orientation. To accommodate such changes, it is known to update the information available to the treatment-planning process during the overall course of a protracted treatment regimen.
Updating the treatment plan can comprise obtaining a new image of the patient's relevant anatomy prior to a given treatment session. One can then employ deformable registration techniques to modify a treatment plan that presumes a first (earlier) anatomical configuration to now correlate to a present anatomical configuration for the patient. Unfortunately, typical deformable registration practices are computationally intensive (in order to accurately accommodate the numerous ways in which a patient's anatomy can vary from a prior presentation) and this can lead to expensive equipment requirements, treatment delay, or both.
Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. Certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. The terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein.